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1 March 2006 Land-based Census of Wintering Waterfowl: Reliability and Conservation Implications
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The International Waterbird Census (IWC) is one of the longest-running bird monitoring schemes in the Western Palearctic. Most of its data are collected with land-based counts, the reliability of which is largely unknown. This study compared estimates of land-based vs. aerial counts, and the relative conservation values of coastal sites obtained with the two methods. The data were collected in the West-Estonian archipelago of the Baltic Sea in 1993, and analyzed at two spatial scales (mean area of plots 9 and 36 km2). Among nine waterfowl species, land-based and aerial census provided closely correlated local population estimates for the Mute Swan (Cygnus olor), Steller’s Eider (Polysticta stelleri), Long-tailed Duck (Clangula hyemalis) and, at the larger scale, for the Mallard (Anas platyrhynchos). However, small numbers of all species, except the swan, remained undetected with the land-based census, and numbers of Mallard and Steller’s Eider were also systematically underestimated. The areas having the highest conservation value were reliably identified with the land-based census, particularly at the larger scale. Hence, land-based studies are in general accordance with the aims of the IWC, but the absolute population estimates should be interpreted with care.

Hannes Pehlak, Asko Lõhmus, Andres Kuresoo, and Leho Luigujõe "Land-based Census of Wintering Waterfowl: Reliability and Conservation Implications," Waterbirds 29(1), 76-80, (1 March 2006).[76:LCOWWR]2.0.CO;2
Received: 20 May 2005; Accepted: 1 October 2005; Published: 1 March 2006

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